In oil and gas, geothermal drilling, mining, or construction of boreholes, a hole or borehole is drilled deep within the earth for exploration, extraction, or injection of resources such as water, gas, or oil, or for installing cables, fibre, or pipelines (e.g., in construction). Boreholes may be formed using a drill string, wherein sections of drill pipe are connected to a drill bit.
The drill string may include a measurement while drilling (MWD) system having sensors packaged in a section of the drilling string. For example, in some MWD systems, the sensors may be packaged in a section of the drill string near the drill bit. These sensors are generally used to measure parameters or properties of the drilling system, borehole, or formation. In one specific application, the sensors may be used to survey boreholes using downhole survey instruments. The instruments typically contain sets of accelerometers and magnetometer(s) or gyroscope(s) that are coupled within a bottom hole assembly (BHA), which in turn is coupled in the drill string. The survey instruments are used to measure the direction and magnitude of the local gravitational and magnetic field vectors in order to determine the azimuth and the inclination of the borehole at each survey station within the borehole. Generally, discrete borehole surveys are performed at survey stations along the borehole when drilling is stopped or interrupted to add additional joint or stands of drill pipe to the drill string at the surface.
Sensing modules are also used to provide operators with information regarding the drilling operation as the drilling progresses. In such operations, information regarding the drilling system, borehole, and/or formation characteristics may be provided to an operator in close to real time. Such information may include toolface, shock & vibration, resistivity, radioactivity, porosity, density, and the like.
With MWD operations, the downhole component(s) of the MWD system(s) generally transmit the information to the surface component of the MWD system for analysis. For example, information may be transmitted using mud pulse telemetry, electromagnetic communications, acoustic communications, and/or the like.
Typical drilling activity induces various types of noise, such as vibration or magnetic interference. The noise may be detrimental to the precise measurements needed to obtain a borehole survey. As such, in a typical MWD system, the survey is acquired at particular intervals at which the MWD system autonomously determines drilling activity has been paused. Within the prior art, most systems monitor the state of mud pumps (located on the surface) to determine if activity has been paused.
Mud pumps circulate fluid through the drill string and back around the annular space between the drill string and the borehole. Fluid circulated through this hydraulic circuit is intended to lubricate the drill string and clean drill cuttings from the borehole.
The MWD system usually processes measurements from pressure sensors, accelerometers or flow sensors to determine the state of the mud pump(s). For example, changes in ambient pressure, pressure differential, pressure signatures unique to the mud pumps, and the like, may be used to determine the state of the mud pump. Additionally, fluid flow through or around the MWD system may also induce acoustic noise, vibrations, and the like, that may be used to determine the state of the mud pump in some MWD systems.
In drilling operations, the state at which mud pumps are ‘off’ (i.e., not circulating fluid through and around the drill string), is sometimes referred to as the ‘flow off’ state, as drilling fluid is generally not circulating or flowing through the mud pump system. A ‘flow on’ state is therefore one at which the mud pump system is presumably ‘on’ and drilling fluid is circulating or flowing.
In some drilling operations, the mud pump system may be maintained in a “flow on” state in order to lubricate and/or clean the borehole. For example, the mud pump system may be maintained in a “flow-on” state to prevent the drill string from getting stuck within the borehole, or to manage the drilling system pressure (i.e., managed pressure drilling).
In a lost circulation event, a significant amount of fluid may continue to flow through or around the MWD system, even when the mud pump system is in a “flow off” state at the surface. That is, the MWD system may continue to determine a “flow on” state, and as such, will not acquire a survey even if needed. There is also an assumption that in the “flow off” state, the environment is quiet enough to obtain a high quality survey. Even if a “flow off” state is determined, errors from motion due to lost circulation, drill string unwinding, motion interference, or magnetic interference may still lead to a survey not being acquired or to an inaccurate survey.
Even further, improvements in telemetry within the art may permit real-time transmission of data; however, not all data may be sent at once, and as such, decisions on what data to send in real time becomes a consideration. For example, the more data sent uphole, the slower the update rate of each measurement, limiting access to the right data at the right time.